The present invention relates to an optical instrument for inspecting the eye fundus, including visible targets for orienting the visual line of the eye to be inspected along the desired direction.
The optical instrument for examining the eye fundus is so designed that the image of the eye fundus of the eye to be inspected is formed by means of the imaging lens system whereby the formed image is directly observed through the eye piece or recorded on the photographic film. Thus in order to inspect a desired part of the eye fundus, it is necessary that there should be a corresponding angle between the imaging lens system and the visual line of the eye to be inspected. Further in case a plural number of the parts of the eye fundus are to be inspected, it is necessary that the visual line of the eye to be inspected should be oriented along a plural number of the directions in accordance with the number of the parts to be observed. Thus, the eye fundus inspection device is provided with a visual target in order that the visual line of the eye to be inspected could be oriented along the direction corresponding to the parts of the eye fundus to be inspected. The visual line of the eye to be inspected is oriented along the desired direction while the patient observes the visual target.
On the other hand, in the case of the conventional eye fundus inspection device, such as an eye fundus camera, the above mentioned visual target is generally provided movably outside of the frame of the device body. The patient observes the visual target manually brought into a proper position by the operator, whereby the target is observed by the eye of the patient, not opposite to the imaging lens system. Thus the fact that the visual lines of both eyes move corresponding to each other is made use of. The operator should judge the angle between the visual line of the eye to be inspected and the optical axis of the imaging lens system by means of the relation of the other eye than that to be inspected to the target, which is correlatively independent of the relation of the eye to be inspected to the imaging lens system so that it is difficult to decide the position at which the target is provided. If the patient is squint-eyed, it is furthermore difficult for the operator to decide the position. It is also troublesome work for the operator to carry out the focussing operation of the imaging lens system and at the same time to bring the target into the proper position with the hand stretched.